Electric heating device.



F. BERRY. ELECTRH HEATING DEVICE.

APPLICATiON HLED JULY 8.1918.

1,287,1 92. Patented Dec. 10, 1918.

Inventor-z Arthur" Francis Berr g,

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UNITED STATES Parana ARTHUR FRANCIS BERRY, OF LONDON, ENGLAND, ASSIGNORTO GENERAL ELECTRIE! COMPANY, A CORPORATION'OF NEVT YORK.

ELECTRIC HEATING DEVICE.

Specification of Letters Patent.

Patented Dec. 10, 1918.

Application filed July 8, 1918. Serial No. 243,764.

To all whom it may concern Be it known that I, ARTHUR FRANoIs BERRY, asubject of the King of Great Britain, residing at London, England, haveinvented certain new and useful Improyements in Electric HeatingDevices, of which the following is a specification.

This invention has reference to that kind of electrical heating elementsuitable for cooking and similar heating apparatus, wherein a length ofbare strip or wire of resistance metal or alloy (hereinafter referred toas a resistance strip) is arranged between sheet material of arefractory and insulating character, such as sheet mica, and inclosedwithin or backed by, it may be, sheet or plate metal, and particularlyto a heating element of this kind, in which the resistance strip isarranged wholly or mainly at one side of refractory sheet insulatingmaterial of the kind referred to and hereinafter called for distinctionthe outer sheet and is separated from'the surface of the metal body tobe heated by similar refractory sheet insulating material, hereinaftercalled for distinction the inner sheet. Adjacent to the outer sheet ofrefractory insulating material is or may be arranged one or more sheetsof similar material. Example of heating elements of the kind referred toare described in the specification of my British Patents, Nos. 4672/09,14699/18 and 12551/14.

In such heating elements the refractory sheet insulating material usedhas been clear sheet mica. While the use of this material isadvantageous forthe inner sheet next to the surface of themetal body, tobe heated, (hereinafter called for distinction the hot plate), becauseit admits of heat passing therethrough as radiant heat and by conductionto the hot plate against which it is'firmly pressed, the use of suchclear sheet mica for the outer sheet is disadvantageous when it is notdesired to transmit heat outward from the resistance strip to a metalback plate because owing to its being smooth and clear, it has acomparatively low emissivity for heat. Consequently, when the heatingelement is in action, although such outer sheet will be raised toatemperature approaching nearly to that of the resistance strip incontact'therewith, it will not radiate its acquired heat very rapidly tothe hot plate and consequently will not readily take up and rapidly andusefully dissipate the heat of the resistance strip so as to enable suchstrip to be run at such high power as is usually desirable for efficientworking in apparatus such as electrical cooking and like apparatus.

Now the present invention has for object to enable the outer sheet ofrefractory insulating material to rapidly acquire heat from the hotresistance strip and quickly radiate it from those parts of its surfacethat are not covered by the resistance strip through the inner strip tothe hot plate and in this way enable the resistance strip to be Workedat a higher power and in a more economical manner than heretofore usual.

For this purpose the outer sheet of refractory insulating material isconstructed of material adapted rapidly to radiate through the innersheet of refractory mate rial the heat that it acquires from the hotresistance strip. To this end there is employed an outer sheet having amat, roughened or dulled surface on the side next to the length ofresistance strip so that it will rapidly radiate inward toward the hotplate, the heat which it takes up from the resistance strip. Theopposite side or surface of such sheet, which will usually be of mica,and.is hereinafter referred to as mica, is smooth and clear so that itwill have a low emissivity in a backward direction unless it is desiredto also heat a back plate in which case the rear surface of the outersheet may also be of a mat, roughened 0rdulled character. The sheet micaused for such outer sheet may have the mat, roughened or dull surfaceexisting naturally thereon, or such a surface may be produced thereonartificially, as by treating one surface of clear sheet mica chemically,as with a suitable acid or other corroding agent. or mechanically, forexample, by abrasion, as by rubbing it with powdered glass or emery.

In the accompanying illustrative drawings Figure 1 shows in section, aportion of one construction of electrical heating element of the kindherein referred to embodying the invention. Fig. 2 is a face View of aportion of an outer sheet of mica with resistance strip thereon.

Fig. 3 is a section showing the electrical heating element appliedbetween a hot plate to be heated and a back or holding plate. Fig. 4: isa similar view to Fig. 3 but showresistance strip 1 designed to beheated by' the passage therethrough of an electriccur- 7 rent and twosheets 2 and 8 of mica between which the strip 1 is held. In Fig. 3 theheating element is held against one side of a metal plate 4 to be heatedby a back plate 5 that may be of metal or refractory insulatingmaterial. according to circumstances, the sheet'2 being what is hereincalled the inner sheet and 3 the outer sheet. The resistance strip 1 inthe example shown is mounted on the outer sheet 3 of mica after themanner described in the specification of former Letters Patent grantedto me No. 8829 of 1915 so that it is mainly on the inner surface of thesaid outer sheet of mica. This inner surface of the outer sheet 3 ofmica, which is pressed closely against the heating strip 1 has a mat,roughened or dull surface for the purpose hereinbefore explained. As theouter sheet 3 of mica will, by reason of its being in close contact withthe re sistance strip 1, be heated to almost the same temperature as theresistance strip and as the portion of its mat, roughened or dulledsurface not covered by the resistance strip forms a large proportion ofsuch surface, say thereof, such portion, owing to its high emissivity,will act rapidly to transmit or dissipate the heat of the resistancestrip 1 and outer sheet 3 through the inner sheet 2 of mica to the hotplate 4 and thus allow of the resistance strip being worked at a highpower. The opposite or outer surface of the said outer sheet 3 is, inthis example,

smooth or clear. The inner sheet 2 may be of clear or transparent micaso as to admit of radiant heat from the outer sheet 3 passing through itto the hot plate, and also of the passage by conduction, of heatdirectly received from the resistance strip 1 which is in direct contacttherewith. To admit of this inner sheet absorbing and transmitting in abetter or quicker manner heat obtained from the outer sheet 3 andresistance strip 1 to the hot plate l, its outer surface, namely thatnext the outer'sheet 3 and resistance strip 1,,mayalso be of a mat,roughened or dulled character.

Loss of heat from the outer side of the outer sheet 3 of mica may, whendesired, be prevented in any known or suitable way. In Fig. 4 refractorynonconducting material 6, for instance slag woo-l, is for this purpose,arranged between the outer sheet 3 and a back plate 5.

7 What I claim as new and desire to secure by Letters Patent of theUnited States, is

1. An electrical heating element of the kind herein referred to, havingan outer sheet of refractory insulating material with a mat, roughened0r dulled surface facing toward the inner sheet and bearing directlyagainst the resistance strip of the element, substantially as described.

2. An electrical heating element of the kind herein referred to,comprising inner and outer sheets of mica and a resistance strip clampedbetween and in direct contact with such sheets, the inner surface of theouter sheet having a mat, roughened or dull surface bearing against theresistance strip, substantially as described.

3. A heating element according to the preceding claims, wherein theopposite or outer surface of the outer sheet of mica is smooth andclear, substantially as described.

4:. An electrical heating element according to any of the precedingclaims, wherein the outer surface of the inner sheet opposite theresistance strip and outer sheet has-a mat, roughened or dulled surface,substantially as described. 7 V

5. In electrical heating apparatus, electrical heating elementsembodying sheet mica having mat, roughened or dulled surfaces,substantially as described for the pup poses set forth.

In witness whereof, I have hereunto set my hand this 19" day of June,1918.

ARTHUR FRANCIS BERRY.

Copies of this patent may be obtained for five cents each, by addresslngthe Commissioner-of ratente,

' Washington, D. G. I

